Grid for radiography and manufacturing method thereof, and radiation imaging system

ABSTRACT

In an X-ray imaging system, first and second grids are disposed between an X-ray source and an X-ray image detector, and produce fringe images. From the fringe images, phase change information of X-rays is obtained. The phase change information provides contrast for an X-ray image. The first and second grids have similar configuration. Each grid is constituted of a grid layer and a support member. The grid layer includes X-ray absorbing portions and X-ray transparent portions arranged alternately in one direction. Each X-ray transparent portion contains hollow space having air trapped therein, for the purpose of reducing an X-ray absorption loss.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a grid for radiography using radiation,and a manufacturing method of the grid, and a radiation imaging system.

2. Description Related to the Prior Art

When radiation e.g. X-rays is incident upon an object, the intensity andphase of the X-rays are changed by interaction between the X-rays andthe object. At this time, the phase change of the X-rays is larger thanthe intensity change, in general. Taking advantage of these propertiesof the X-rays, X-ray phase imaging is developed and actively researched.In the X-ray phase imaging, a high-contrast image (hereinafter calledphase contrast image) of a sample is obtained based on the phase changeof the X-rays caused by the sample, even if the sample has low X-rayabsorptivity.

As a type of the X-ray phase imaging, there is devised an X-ray imagingsystem using the Talbot effect, which is produced with two transmissivediffraction gratings (refer to U.S. Pat. No. 7,180,979 corresponding toJapanese Patent No. 4445397, and Applied Physics Letters Vol. 81, No.17, page 3287 written by C. David et al. on October 2002, for example).In this X-ray imaging system, a first grid is disposed behind a samplewhen viewed from the side of an X-ray source, and a second grid isdisposed downstream from the first grid by the Talbot distance. Behindthe second grid, an X-ray image detector is disposed to detect theX-rays and produce the phase contrast image. Each of the first andsecond grids has narrow X-ray absorbing portions and X-ray transparentportions, which are arranged parallel to one another with aligning theiredges. The Talbot distance refers to a distance at which the X-rayspassed through the first grid forms a self image (fringe image) by theTalbot effect. The fringe image formed by the Talbot effect is modulatedby the interaction (phase change) between the sample and the X-rays.

In the above X-ray imaging system, a moire pattern, which is produced bysuperimposition (intensity modulation) of the second grid on the selfimage of the first grid, is detected by a fringe scanning method inorder to obtain phase information of the sample, that is, changes inphase of the X-rays due to the sample. In the fringe scanning method, animage is captured whenever the second grid is translationally movedrelative to the first grid in a direction approximately parallel to asurface of the first grid and approximately orthogonal to a griddirection of the first grid by a scan pitch that is an integralsubmultiple of a grid pitch. From a change of each and every pixel valuedetected by the X-ray image detector, angular distribution (adifferential phase image) of the X-rays refracted by the sample isobtained. Then, a phase contrast image of the sample is obtained basedon the angular distribution. The fringe scanning method is available inan imaging system using laser light, instead of the X-rays (refer toApplied Optics Vol. 37, No. 26, page 6227 written by Hector Canabal etal. on September 1998, for example).

The first and second grids require high X-ray absorptivity at theirX-ray absorbing portions. The X-ray absorbing portions of the secondgrid, in particular, require higher X-ray absorptivity than those of thefirst grid, to reliably apply the intensity modulation to the fringeimage. Thus, the X-ray absorbing portions of the first and second gridsare made of gold (Au) with high atomic weight. Also, the X-ray absorbingportions of the second grid need to have relatively large thickness(high aspect ratio) in a propagation direction of the X-rays. As aresult, the second grid has such a fine configuration that the X-rayabsorbing portions have a pitch of several micrometers and a thicknessof several tens to a hundred and several tens micrometers.

The X-ray transparent portions of the first and second grids, on theother hand, require a low X-ray absorption loss. The X-ray transparentportions are conventionally formed of an insulating substance such assilicon oxide, resin, or LPD ceramic (refer to the U.S. Pat. No.7,180,979). In another case, the X-ray absorbing portions are arrangedat constant distance with leaving gaps therebetween, so that the gapsfunction as the X-ray transparent portions (refer to Japanese PatentLaid-Open Publication No. 2009-0142528).

However, in the case of making the X-ray transparent portions out of thesilicon oxide or the LPD ceramic, as described in the U.S. Pat. No.7,180,979, the X-ray absorption loss arises because these substanceshave the X-ray absorptivity. The X-ray absorptivity of the resin islower than those of the silicon oxide and the LPD ceramic, but still notzero. Therefore, the X-ray absorption loss still arises with use of theresin.

In the case of leaving the gaps between the adjoining X-ray absorbingportions, as described in the Japanese Patent Laid-Open Publication No.2009-042528, since the X-ray absorbing portions have a high aspectratio, more specifically have a width of several micrometers and athickness of the order of 100 micrometers, the X-ray absorbing portionsfall and incline in its width direction. This results in degradation ingrid performance, and thus this method is unrealistic.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a grid having radiationtransparent portions with a low radiation absorption loss, amanufacturing method of the grid, and a radiation imaging system usingthe grid.

To achieve the above and other objects, a grid for radiography accordingto the present invention includes a plurality of radiation absorbingportions made of a radiation absorbing material, and a plurality ofradiation transparent portions made of a radiation transparent materialcontaining hollow space. The radiation absorbing portions and theradiation transparent portions are alternately arranged.

The hollow space is preferably formed of air bubbles dispersed in theradiation transparent material, or hollow beads dispersed in theradiation transparent material. The radiation transparent material ispreferably a resin paste.

The grid may further include a reinforcing layer formed between theradiation absorbing portion and the radiation transparent portion, or asupport member formed integrally with the radiation transparentportions.

In the grid, each of the radiation absorbing portions and the radiationtransparent portions preferably extends in a first direction. Theradiation absorbing portions and the radiation transparent portions arepreferably arranged alternately in a second direction orthogonal to thefirst direction.

A manufacturing method of the grid includes the steps of forming a seedlayer on a surface of abase substrate; first etching the base substrateon a side of the seed layer through a first etching mask, to form firstgrooves; depositing a radiation transparent material in each firstgroove so as to make hollow space inside the first groove, to formradiation transparent portions; second etching the base substrate on aside opposite from that of the first etching step, using the radiationtransparent portions as a second etching mask, to remove the basesubstrate from between the radiation transparent portions and formsecond grooves having the seed layer at each bottom; and charging aradiation absorbing material into the second grooves by electrolyticplating using the seed layer as an electrode, to form radiationabsorbing portions.

In a radiation imaging system according to the present invention, thegrid described above is used as at least one of the first and secondgrids.

According to the grid for radiography of the present invention, theradiation transparent portion contains the hollow space with low X-rayabsorptivity, and hence has the low radiation absorption loss. Since theradiation imaging system according to the present invention uses thegrid having the low radiation absorption loss at its radiationtransparent portions, the contrast of a fringe image is improved. As aresult, it is possible to obtain a phase contrast image with high imagequality.

BRIEF DESCRIPTION OF THE DRAWINGS

For more complete understanding of the present invention, and theadvantage thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of an X-ray imaging system according to afirst embodiment;

FIG. 2 is a plan view of a second grid;

FIG. 3 is a cross sectional view of the second grid;

FIG. 4 is an explanatory view of a first step in a manufacturing processof the second grid;

FIG. 5 is an explanatory view of a second step in the manufacturingprocess of the second grid;

FIG. 6 is an explanatory view of a third step in the manufacturingprocess of the second grid;

FIG. 7 is an explanatory view of a fourth step in the manufacturingprocess of the second grid;

FIG. 8 is an explanatory view of a fifth step in the manufacturingprocess of the second grid;

FIG. 9 is an explanatory view of a sixth step in the manufacturingprocess of the second grid;

FIG. 10 is an explanatory view of a seventh step in the manufacturingprocess of the second grid;

FIG. 11 is an explanatory view of an eighth step in the manufacturingprocess of the second grid;

FIG. 12 is an explanatory view of a ninth step in the manufacturingprocess of the second grid;

FIG. 13 is a cross sectional view of a second grid according to a secondembodiment; and

FIG. 14 is a cross sectional view of a second grid according to a thirdembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

As shown in FIG. 1, an X-ray imaging system 10 is constituted of anX-ray source 11, a first grid 13, a second grid 14, and an X-ray imagedetector 15. The X-ray source 11 has a rotation-anode type X-ray tubeand a collimator for limiting an irradiation field of X-rays, forexample, and applies the X-rays to a sample H. The first and secondgrids 13 and 14, being of an X-ray absorptive type, are opposed to theX-ray source 11 in a Z direction corresponding to an X-ray propagationdirection. The first grid 13 is disposed at a certain distance away fromthe X-ray source 11 so as to place the sample H therebetweeen. The X-rayimage detector 15 is a flat panel detector (FPD) composed ofsemiconductor circuitry, for example, and is disposed behind the secondgrid 14.

The first grid 13 is provided with plural X-ray absorbing portions 13 aand X-ray transparent portions 13 b, which extend in a Y direction beingone direction in a plane orthogonal to the Z direction. The X-rayabsorbing portions 13 a and the X-ray transparent portions 13 b arealternately arranged in an X direction orthogonal to both the Z and Ydirections, so as to form a grid with a stripe pattern. As with thefirst grid 13, the second grid 14 is provided with plural X-rayabsorbing portions 14 a and X-ray transparent portions 14 b, whichextend in the Y direction and are alternately arranged in the Xdirection.

Now, the configuration of the second grid 14 will be described. Notethat, the first grid 13 has a configuration similar to that of thesecond grid 14, except for the width and pitch of the X-ray absorbingportions 13 a in the X direction, the thickness of the X-ray absorbingportions 13 a in the Z direction, and the like. Thus, the detaileddescription of the first grid 13 is omitted.

FIG. 2 is a plan view of the second grid 14 viewed from the side of theX-ray source 11. FIG. 3 shows a cross sectional view taken along lineIII-III of FIG. 2. The second grid 14 has a grid layer 20 including theX-ray absorbing portions 14 a and the X-ray transparent portions 14 b,and a support member 21 for supporting the grid layer 20. The X-rayabsorbing portions 14 a are made of metal with high X-ray absorptivity,such as gold (Au) or platinum (Pt).

The X-ray transparent portions 14 b and the support member 21 are madeof X-ray transparent material such as silicon nitride (SiN). Each X-raytransparent portion 14 b contains hollow space 22 in which air havinglow X-ray absorptivity is trapped. The hollow space 22 preferablyoccupies one-tenth or more volume within an area corresponding to asingle pixel (approximately 150 μm square) of the X-ray image detector15. Note that, the hollow space 22 may contain gas other than air, suchas nitrogen, oxygen, or hydrogen. The inside of the hollow space 22 maybe vacuumed to further reduce the X-ray absorption loss.

The width W₂ and arrangement pitch P₂ of the X-ray absorbing portion 14a in the X direction depend on the distance between the X-ray source 11and the first grid 13, the distance between the first grid 13 and thesecond grid 14, the arrangement pitch of the X-ray absorbing portions 13a of the first grid 13, and the like. By way of example, the width W₂ isapproximately 2 to 20 μm, and the arrangement pitch P₂ is in the orderof 4 to 40 μm being twice the width W₂. The thickness T₂ of the X-rayabsorbing portion 14 a in the Z direction is in the order of 100 μm, inconsideration of vignetting of a cone beam of X-rays emitted from theX-ray source 11. In this embodiment, the second grid 14 has a width W₂of 2.5 μm, an arrangement pitch P₂ of 5 μm, and a thickness T₂ of 100μm, for example.

Next, the operation of the X-ray imaging system 10 will be described.When the X-rays emitted from the X-ray source 11 pass through the sampleH, phase difference arises in the X-rays. Subsequently, a fringe imageis formed by transmitting the X-rays through the first grid 13. Thefringe image includes transmission phase information of the sample H,which is determined by the refractive index of the sample H and thelength of a transmission optical path.

The intensity of the fringe image is modified by transmitting throughthe second grid 14. Then, the fringe image after the intensitymodulation is detected by, for example, a fringe scanning method. To bemore specific, the second grid 14 is translationally moved relative tothe first grid 13 at a scan pitch that is an equal division (forexample, one-fifth) of a grid pitch in the X direction, which is along agrid surface with respect to an X-ray focus. During this translationalmovement of the second grid 14, the X-ray source 11 applies the X-raysto the sample H, and the X-ray image detector 15 captures plural fringeimages. Then, a differential phase image (corresponding to angulardistribution of the X-rays refracted by the sample H) is obtained from aphase shift amount (a shift amount in phase between in the presence ofthe sample H and in the absence of the sample H) of pixel data of eachpixel detected by the X-ray image detector 15. Integrating thedifferential phase image along a fringe scanning direction allowsobtainment of a phase contrast image of the sample H.

Next, a manufacturing method of the second grid 14 will be described.Note that, since the first grid 13 is manufactured in the same way,detailed explanation about a manufacturing method of the first grid 13is omitted. FIGS. 4 to 12, which show a manufacturing process of thesecond grid 14, are cross sectional views along an XZ plane defined bythe X and Z directions. In a first step, as shown in FIG. 4, a seedlayer 31 made of Au is formed on a surface of a silicon (Si) basesubstrate 30 by sputtering or chemical vapor deposition (CVD).

In a second step, an etching mask is formed on the top of the basesubstrate 30 using a generally known photolithography technique. Asshown in FIG. 5, a resist layer 32 is formed on a surface of the seedlayer 31. To form the resist layer 32, for example, the step of applyinga liquid resist to the surface of the seed layer 31 by spin coating orthe like, and the step of vaporizing an organic solvent from the appliedliquid resist by baking or the like are carried out.

In a third step, as shown in FIG. 6, light e.g. ultraviolet rays isapplied to the resist layer 32 through a photomask 33, which has astripe pattern with lines at the pitch P₂. Then, in a fourth step, asshown in FIG. 7, exposed portions of the resist layer 32 is removed by adeveloping solution. Remaining portions (unexposed portions) of theresist layer 32 compose an etching mask 34 with the stripe pattern thathas lines extending in the Y direction and arranged in the X direction.Each line of the etching mask 34 has a width of 2.5 μm, and theclearance between the lines has a width of 2.5 μm, for example. Notethat, the resist layer 32 is formed of a positive resist, but may bemade of a negative resist. Instead of the etching mask composed of theresist layer, a metal etching mask or the like is usable.

Next, in a fifth step, as shown in FIG. 8, a plurality of grooves (firstgrooves) 35, which extend in the Y direction and are arranged in the Xdirection, are formed in the seed layer 31 and the base substrate 30 bydry etching using the etching mask 34. After that, the etching mask 34is removed by asking. To form the deep grooves 35 with a high aspectratio, deep dry etching is carried out. As the deep dry etching, amethod called Bosch process is used by which the etching and thedeposition of a protective film are performed alternately andrepeatedly.

In the Bosch process, the etching is performed using a SF₆ gas foretching silicon and a C₄F₈ gas for forming the protective film. Sincethe SF₆ gas promotes the etching not only in a depth direction but alsoin a lateral direction, a deep hole or groove cannot be formed only withuse of the SF₆ gas. Thus, in the Bosch process, the SF₆ gas is switchedinto the C₄F₈ gas after the etching is carried out for predeterminedtime, to deposit a CFn polymer produced by plasma. The CFn polymer formsthe protective film on the etched grooves. After that, the etching isperformed again using the SF₆ gas. Since side faces of the groove areetched at lower etching speed than a bottom face of the groove, only thebottom face is etched. Repeating the above steps allows formation of thedeep grooves with the high aspect ratio.

The Bosch process is carried out on etching conditions that, forexample, gas pressure is 1 to 10 Pa, a switching interval between theSF₆ gas and the C₄F₈ gas is in the order of 5 to 10 seconds, and poweris 600 W. Under these conditions, the etching speed is 2 μm/min, and thedepth T₂ of the groove 35 is 100 μm, for example. In this etching, theformation of the high density plasma is of primary importance. There arevarious methods for forming the high density plasma, including a methodusing inductively coupled plasma (ICP), a method using helicon waves,and the like. Note that, the grooves may be formed by wet etchingconsidering plane orientation of a silicon single crystal, instead ofthe dry etching.

Next, in a sixth step, as shown in FIG. 9, an insulating X-raytransparent material 36 made of silicon nitride (SiN) is deposited inthe grooves 35 by the CVD. At this time, the X-ray transparent material36 is charged into each groove 35 with leaving hollow space 22 therein,due to the high aspect ratio of the groove 35. The hollow space 22easily occurs, when a charging speed of the X-ray transparent material36 by the CVD is increased. Thus, controlling the charging speed of theX-ray transparent material 36 allows adjustment of the size of thehollow space 22.

The X-ray transparent material 36 deposited in the grooves 35 composesthe X-ray transparent portions 14 b. The X-ray transparent material 36is deposited on the entire seed layer 31 so as to compose the supportmember 21, in addition to being charged into the grooves 35. The hollowspace 22 is not necessarily continuous in the Y direction, but may bedivided at random intervals depending on manufacturing conditions andthe like.

In a next seventh step, as shown in FIG. 10, a structure of FIG. 9 isturned upside down. The surface of the base substrate 30 is polishedflat by chemical mechanical polishing (CMP), until the X-ray transparentmaterial deposited in the bottom of the grooves 35 is exposed outside.Then, as shown in FIG. 11, in an eighth step, the base substrate 30 isetched and removed using the X-ray transparent material 36 as theetching mask. Thus, grooves (second grooves) 37 are formed between theX-ray transparent portions 14 b, and the seed layer 31 is exposed fromthe bottom of each groove 37. In etching the base substrate 30 using theX-ray transparent material 36 as the etching mask, as described above,an etching rate of the X-ray transparent material 36 has to be lowerthan that of the base substrate 30. The composition of the X-raytransparent material 36 and the base substrate 30 may be determinedbased on a selection ratio (ratio between the etching rates) in the dryetching carried out in this step.

In a next ninth step, as shown in FIG. 12, an X-ray absorbing material38 made of gold (Au) is embedded in the grooves 37 by electrolyticplating using the seed layer 31 as an electrode. The seed layer 31 andthe X-ray absorbing material 38 compose the X-ray absorbing portions 14a. In the electrolytic plating, a current terminal is connected to theseed layer 31. The seed layer 31 disposed in the bottom of every groove37 is preferably linked outside the grooves 37 so as to be connectableto the current terminal at a single position, though it is not shown inthe drawing.

In the electrolytic plating, a structure of FIG. 11 having the X-rayabsorbing material 36 and the seed layer 31 is immersed in a platingsolution, and an anode is opposed to the seed layer 31 therein. Then, byflowing electric current between the seed layer 31 and the anode, metalions contained in the plating solution are deposited on the seed layer31. Thereby, the grooves 37 are filled with Au. In the electrolyticplating of Au, for example, cyanide gold plating, KAu(CN)₂ is used as aplating solution, and KH₂PO₄ or KOH is added as a pH buffer material,such that the plating solution has a pH of 6 to 8. The plating solutionhas a temperature of 25 to 70° C. The density of the electric current is0.2 to 1 A/cm², and Pt-plated Ti is used as the anode. Note that, theabove conditions of the Au plating are just one example, and the Auplating can be carried out with another plating solution and on otherconditions.

Through the manufacturing process described above, the second grid 14having the grid layer 20 and the support member 21 is completed. In theabove embodiment, SiN is used as the X-ray transparent material 36, butan organic material such as polyimide or poly-para-xylylene, or aninorganic material such as SiO₂ or SiC is available. To vacuum theinside of the hollow space 22, the X-ray transparent material 36 may bedeposited in a vacuum environment by the CVD.

Now, other embodiments of the present invention will be described. Inthe following embodiments, the same reference numerals as those of thefirst embodiment indicate the same components, and detailed descriptionof them is omitted. In the following embodiments, a first grid hasconfiguration similar to a second grid except for a grid pitch, athickness, and the like, and is manufactured by a similar process. Thus,detailed description of the first grid is omitted.

Second Embodiment

FIG. 13 shows a cross section of a second grid 40 according to thisembodiment taken along the XZ plane. The second grid 40 includes a gridlayer 41 and the support member 21. The grid layer 41 has the X-rayabsorbing portions 14 a and the X-ray transparent portions 14 b arrangedalternately in the X direction, and a reinforcing layer 42 formedbetween the X-ray absorbing portion 14 a and the X-ray transparentportion 14 b. The reinforcing layer 42 is formed between the X-rayabsorbing portion 14 a and the support member 21.

The reinforcing layer 42 is preferably formed of a material with highX-ray transparency and high stiffness, for example, SiO₂. In a casewhere the X-ray transparent portions 14 b are made of the organicmaterial such as resin, there is a possibility of deformation of theX-ray transparent portions 14 b. The reinforcing layer 42 has the highstiffness enough to maintain the shape of the X-ray transparent portions14 b and prevent the deformation thereof. Also, the reinforcing layer 42prevents the corrosion of the X-ray absorbing portions 14 a due to theorganic material composing the X-ray transparent portions 14 b.

In a manufacturing process of the second grid 40, the step of formingthe reinforcing layer 42 may be added between the fifth step shown inFIG. 8 and the sixth step shown in FIG. 9 in the manufacturing method ofthe second grid 14 according to the first embodiment. The reinforcinglayer 42 is formed so as to cover the bottom and side faces of thegrooves 35 and the surface of the seed layer 31 by the CVD. The othersteps of the manufacturing process are the same as those of the firstembodiment, and the detailed description thereof is omitted.

Third Embodiment

FIG. 14 shows a cross section of a second grid 50 according to thisembodiment taken along the XZ plane. The second grid 50 has a grid layer51 and a support member 52. The grid layer 51 is constituted of theX-ray absorbing portions 14 a and X-ray transparent portions 53 arrangedalternately in the X direction. The X-ray transparent portions 53 andthe support member 52 are made of a resin paste with high X-raytransparency. As the resin paste, for example, an acrylic resin havingair bubbles 53 a dispersed therein is used.

To manufacture the second grid 50, in the sixth step shown in FIG. 9 ofthe manufacturing process of the second grid 14 according to the firstembodiment, the resin paste containing the air bubbles 53 a may becharged into the grooves 35 and dried therein, instead of depositing theX-ray transparent material 36 in the grooves 35 by the CVD. The resinpaste is produced by dispersing a resin material in a solvent. Then, toform the air bubbles 53 a, the resin paste is agitated so as to mix airtherein. The other steps of the manufacturing process are the same asthose of the first embodiment, the detailed description thereof isomitted.

As with the second embodiment, the reinforcing layer may be formedbetween the X-ray absorbing portion 14 a and the X-ray transparentportion 53. Instead of the resin paste having the dispersed air bubbles53 a, a resin paste having hollow resin beads dispersed therein may beused. In this case, there is no need to agitate the resin paste, and themanufacturing process becomes easier.

Other Embodiments

In the above first and second embodiments, the hollow space is formed ineach X-ray transparent portion, and the distribution of the hollow spaceis preferably uniform in an XY plane. However, the hollow space may bedistributed higher at a marginal portion than at a middle portion. Inthis case, the X-ray transparency of the X-ray absorbing portion isincreased with approaching from the center of the grid to its ends. TheX-rays emitted from the X-ray source 11 is the cone beam, and theintensity of the X-rays is decreased with approaching from the center ofthe grid to its ends. Therefore, since the distribution of the X-raytransparency compensates for the intensity distribution of the X-rays,the intensity distribution of the X-rays passed through the X-raytransparent portions of the grid becomes substantially uniform.

If there is too much hollow space in the marginal portion of the grid,the physical strength of the grid is reduced. For this reason, thehollow space may be distributed higher at the middle portion than at themarginal portion, contrarily to above.

In each of the above embodiments, the present invention is explainedwith taking the first and second grids as an example, but the presentinvention is applicable to a source grid, if the source grid is providedon an X-ray emission side of the X-ray source 11.

The first and second grids linearly project the X-rays passed throughtheir X-ray transparent portions. However, the first and second gridsmay diffract the X-rays at their X-ray transparent portions to producethe so-called Talbot effect (similar to U.S. Pat. No. 7,180,979). Inthis case, however, the distance between the first and second grids hasto be set at the Talbot distance. In this case, a phase grating insteadof an absorption grating may be used as the first grid, and the phasegrating used as the first grid projects a fringe image (self image)produced by the Talbot effect to the second grid.

In the above embodiments, the sample H is disposed between the X-raysource and the first grid, but may be disposed between the first gridand the second grid. The phase contrast image can be produced in thiscase, just as with above.

The embodiments described above are applicable to various types ofradiation imaging systems for medical use, industrial use,nondestructive inspection use, and the like. The present invention isapplicable to an anti-scatter grid for removing scattered rays in X-rayimaging. Furthermore, in the present invention, y-rays or the like isusable as radiation instead of the X-rays.

Although the present invention has been fully described by the way ofthe preferred embodiment thereof with reference to the accompanyingdrawings, various changes and modifications will be apparent to thosehaving skill in this field. Therefore, unless otherwise these changesand modifications depart from the scope of the present invention, theyshould be construed as included therein.

1. A grid for radiography comprising: a plurality of radiation absorbingportions made of a radiation absorbing material; and a plurality ofradiation transparent portions made of a radiation transparent materialcontaining hollow space, said radiation absorbing portions and saidradiation transparent portions being alternately arranged.
 2. The gridaccording to claim 1, wherein said hollow space is formed of air bubblesdispersed in said radiation transparent material.
 3. The grid accordingto claim 1, wherein said hollow space is formed of hollow beadsdispersed in said radiation transparent material.
 4. The grid accordingto claim 1, wherein said radiation transparent material is a resinpaste.
 5. The grid according to claim 1, further comprising: areinforcing layer formed between said radiation absorbing portion andsaid radiation transparent portion.
 6. The grid according to claim 1,further comprising: a support member formed integrally with saidradiation transparent portions.
 7. The grid according to claim 1,wherein each of said radiation absorbing portions extends in a firstdirection; wherein each of said radiation transparent portions extendsin said first direction; and said radiation absorbing portions and saidradiation transparent portions are alternately arranged in a seconddirection orthogonal to said first direction.
 8. A manufacturing methodof a grid for radiography comprising the steps of: forming a seed layeron a surface of a base substrate; first etching said base substrate on aside of said seed layer through a first etching mask, to form firstgrooves; depositing a radiation transparent material in each of saidfirst grooves so as to make hollow space inside said first groove, toform radiation transparent portions; second etching said base substrateon a side opposite from that of the first etching step, using saidradiation transparent portions as a second etching mask, to remove saidbase substrate from between said radiation transparent portions and formsecond grooves having said seed layer at each bottom; and charging aradiation absorbing material into said second grooves by electrolyticplating using said seed layer as an electrode, to form radiationabsorbing portions.
 9. A radiation imaging system having a first gridfor transmitting radiation emitted from a radiation source to produce afringe image, a second grid for applying intensity modulation to saidfringe image at plural relative positions having phases different fromthat of a periodic pattern of said fringe image, and a radiation imagedetector for detecting said fringe image after being subjected to saidintensity modulation by said second grid at each of said relativepositions, said radiation imaging system, wherein the grid forradiography according to claim 1 is used as at least one of said firstand second grids.